In the interest of sticking to real facts and avoiding hyperbole, I submit the following information about the exterior walls of the city-state of Vatican City:
Being separated from the city, on the west bank of the Tiber river, the area was an outcrop of the city that was protected by being included within the walls of Leo IV (847–55), and later expanded by the current fortification walls, built under Paul III (1534–49), Pius IV (1559–65) and Urban VIII (1623–44).
Please note that the Vatican's walls are not of recent or even modern construction. The "newest" portion of the Vatican walls are nearly 400 years old. The older sections are nearly 1300 years old.
We would do well to remember that throughout its long history, the Vatican has been attacked from time to time by hostile military forces. The barbaric Germanic tribes invaded Rome in the 5th century. Attila the Hun came next, followed by a Byzantine invasion of Italy under Justinian. There was conflict in the 14th century with the French crown that resulted in the Avingnon Papacy. There were the wars of the Papal States during the Renaissance and Reformation periods. Those walls were needed historically and have served Rome well. To compare those defensive walls with Donald Trump's idea of building a modern version of the Great Wall of China on the southern border of the United States of America is comparing apples to oranges. It just isn't the same. Put it in perspective.
We would do well to remember that today the walls do NOT completely encircle the Vatican. They do still exist on some sides of the Vatican, but not around the approach to St. Peter's Basilica. A white line painted on the ground is all that separates St. Peter's Square from the territory of the nation of Italy. There is no wall, fence, crossing guard or checkpoint there. Anyone can freely cross and a passport is not required.
The pope has given us a lot to ponder in the following comment (Thank you, Father Slusser!): And then, a person who thinks only about building walls, wherever they may be, and not building bridges, is not Christian. This is not in the Gospel.
And if you think about it, the Pope is quite correct. The Gospel teaches us about showing mercy, especially showing mercy to strangers, foreigners, and outcasts. Think of the parable of the Good Samaritan. It is nothing but thinly veiled Social Darwinism to slam the door in people's faces and say, "I have mine. You stay out." That reminds me more of the parable of the Rich Man and Lazarus. Remember how Lazarus sat outside the gates of the Rich Man and how the Rich Man was so cold and callous he didn't even notice Lazarus sitting there, starving and covered in sores? Read the story again and notice who ended up in hell.
Remember our Lord said the love of money is the root of all evil and that it is exceedingly difficult for a rich man to enter heaven. Perhaps our Lord meant exactly what He said, without any sophisticated attempts to explain it all away?
May God have mercy on us all.